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Length of One Day

The length of one day (technically, a solar day) on a planet is the time from noon to noon. Since the planets spin on their axes at different rates and travel about the Sun at different speeds as well, the length of one day is different for each planet. For example, on Earth the length of a solar day is 24 hours. But because of its slow rotation and its rapid orbital speed, one solar day on Mercury lasts about as long as 176 days on Earth.

A Day on Mercury

How long is a day on Mercury? Watch the Sun rise and set on Mercury in the "A Day on Mercury" animation. Click on the image above.

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Mercury not only orbits the Sun in the least amount of time, it also moves the fastest along its orbital path, with an average speed of about 48 km per second. If you could run at that speed you would could run from New York City to Los Angeles in less than 83 seconds!